Advertisement

Advertisement

How Saturn’s tiger moon got its stripes

SATURN is steadily pumping water from its frozen moon Enceladus. Images taken by NASA’s Cassini probe support the idea that Saturn’s gravitational squeezing of the moon causes fissures to widen and contract, controlling how much icy material erupts from the cracks.

Enceladus orbits Saturn in an elongated path, and changes in the strength of the giant planet’s tug create tidal stresses that squeeze and heat the moon’s interior. Ice geysers that erupt from the moon’s south pole (pictured) are thought to be fed by a briny subsurface ocean. These plumes sandblast other nearby moons and are probably the source of one of Saturn’s rings.

Previous calculations had suggested that tidal stress could also be why the amount of material ejected in the plumes varies. To test the idea, Matt Hedman of Cornell University in Ithaca, New York, and his colleagues analysed seven years’ worth of Cassini data.

Looking at the brightness of the plumes and adjusting for the viewing angle, the team found that geyser activity peaks when Enceladus is at its most distant point from Saturn (Nature, DOI&colon; 10.1038/nature12371). That is when the moon experiences the strongest tensile stress, which probably widens the fissures and lets more material escape.

This article appeared in print under the headline “Saturn’s pumping its geyser moon”